In the offset printing of repeated, spaced impressions on a continuous web, such as paper tape used in heading of objects such as paper legal pads or the like, difficulty is encountered in properly spacing the impressions where more than one printing plate is carried on the circumference of the printing plate cylinder. Proper joining of the printed tape to the heading area of the pad in the conventional "stripper" apparatus, so that the printed material is properly oriented on the completed pad, can be accomplished only if accurate spacing of the printed impressions is maintained.
One prior art attempt to overcome the difficulty is disclosed in Crissy U.S. Pat. No. 3,610,147. In the disclosure of the patent the sheet or web to be printed is fed intermittently to a continuously rotating printing cylinder. By utilizing, in contrast, a continuously fed web and an intermittently, rather than continuously, rotated printing plate cylinder, the concept of the present invention provides several distinct advantages. One advantage is that a smaller (in diameter) printing plate cylinder may be utilized. This permits use of smaller printing plates for a given rate of printed tape output resulting in substantial cost saving of the order of 50 percent. Relatively small diameter plate cylinder and correspondingly small printing plates may be used and the required relatively long spacing between series or groups of printed impressions may still be obtained. The printer, utilizing the concept of the present invention, can be placed in-line with respect to the stripper apparatus where the tape and the pads are joined and such an arrangement has hitherto been unknown in the prior art. Two or more printers embodying the present invention may be placed in-line with the stripping apparatus to allow printing in more than one color or to facilitate rapid change-over of print color. Intermittently rotating the printing plate cylinder while continuously moving the web or tape permits printing with a printing cylinder having a circumference smaller than the length of the series or group of printed impressions while still leaving substantial space on the web between each series of printed impressions on the web. Since the plates are not damaged by movement of the tape across them (movement of the tape with relation to the stationary plate cylinder occurs only in a void area between printing plates on the cylinder), the printing plates have an extended useful life, of the order of three hundred thousand impressions, far longer than is the case when the plates are conventionally utilized. The apparatus of the present invention further provides a means for separating the moving tape or web and the printing plates on the plate cylinder whenever a malfunction occurs.
The concept of the present invention further envisages providing a feeding apparatus for feeding pad strips (uncut groups of pads) to the stripper apparatus where the printed tape is applied as a cover-binding to one marginal area of the strips. The feeding apparatus is characterized by two separate, but overlapping endless belt conveyors which are coordinated so that pad strips are fed one-by-one into the stripper apparatus where the printed tape is applied. The arrangement is such that the pad strips may be placed by the operator on the conveyor means in overlapping relation to each other, the effective area under control of the operator thus may accommodate a larger number of objects (pad strips) than would be the case if the objects had to be lined up in prior art, non-overlapping alignment.